J-REORIENTATION IN THE $H_{2}CO\bar{A}^{1}A_{2}4^{1}1_{0,1}$ ROTATIONAL LEVEL

Author Institution: Department of Chemistry, Massachusetts Institute of Technology; Wiess School of Natural Sciences, Rice UniversityWe report measurements of the rate of depolarization of a single rotational level of formaldehyde in the absence of an external field. The level in question is $\bar{A}A_{2} V_{4}=1, J=1, K_{*}=0$. Previous rotational state-to-state measurements in the $H_{2}CO \bar{A}$ state by Transient Gain and Transient Polarization Spectroscopies suggested a remarkable resistance to depolarization, even for $\Delta J=\pm 1.\pm 2$ rationally inelastic processes, and a strong propensity for electric a-dipole collision-induced inelastic transitions. At zero electric field, elastic depolarization within J=1 are dipole forbidden; however. M-changing transitions could occur via two-step $1_{0.1}\rightarrow(O_{0.2} or 2_{0.3})\rightarrow 1_{0.4}$ processes. The transient response within the $1_{g}$, level is monitored by various PUMP and PROBE polarization schemes. The transient gain data are fitted by various master equation models which provide information about the direct vs. sequential nature of the depolarization process